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Name: Jack
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Question:
I am amid a debate on whether water conducts electricity or not. One side says that pure water will not conduct electricity; the other side says that with enough voltage it will. Can you enlighten us? If possible, please explain the differences in water types and what is required to get "pure H2O".



Replies:
Aah, semantic arguments...

With enough voltage (actually, the issue is an intense enough electric field), any conducting material will experience "dielectric breakdown" and allow current to flow. What happens is that the electrons are actually ripped away from their atoms, disrupting the chemical structure of the material.

In the case of pure water, you'd be making a hydrogen/oxygen plasma, which would conduct electricity. But would you call that water?

Richard E. Barrans Jr.,
Department of Physics and Astronomy
University of Wyoming


Commomnly demonstrated in sceince classrooms, using regular US household (110 volt) AC current, pure water seems to fails to complete a circuit in order to light a incandescent light bulb for example. Salts added to the water will result in a complete circuit since they dissociate readily. This demonstration has a purpose in some aspects, however, it often creates a misconception.

Water does dissociate into ions so their is some electricity flowing at all times with even pure water, but not enough to heat up the tungsten element to glow in a common bulb using house current. That said, with enough electron flow, any substance or solution will conduct electricity.

Steve Sample


Absolutely pure water ionizes. The concentration of (H+1) and (OH-1), each having a concentration of 10^-7 mols per liter. This means that "absolutely pure" water will conduct an electrical current, so the determination needs to be carried out in platinum vessels. Atmospheric gases such as N2, O2, and others must be scrupliously removed and not allowed to come into contact with the test sample Should you increase the voltage, other reactions will occur. In practice it is very, very difficult to obtain "absolutely pure" water. Even glass is sufficiently soluble to give a "false positive" signal for conductivity.

There is another problem. If you "purify" the water, by whatever method, a factor is the fractionation of various nuclear isotopes of water, the largest being HDO and D2O.

So what seems like a simple measurement, in practice, becomes very complicated. OH!! remember that all of the parameters above depend upon temperature!!

Vince Calder



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